Natural Gas: A Better Option for Your Standby Application?

Reliable standby power provides protection in the event of power failure. For critical operations, like hospitals, data centers and water treatment plants, continuous power is essential. Standby applications inherently have limited hours of operation because they only kick on when there’s an interruption in power flow from the main source. Therefore, the more hours the dedicated standby system runs, the more important your fuel choice becomes.

The standby market is generally dominated by diesel-fueled generator sets because they can be installed with lower capital investment (per power output), and typically provide better transient (load acceptance) capabilities. Nevertheless, natural gas generator sets are gaining popularity for reliable standby power solutions thanks to ease of maintenance and reduced emissions compared to traditional diesel fuels.

Applications which may be better suited for natural gas standby gensets include:

Sites subject to tighter emission requirements

Areas that endure frequent and/or dangerous storms (hurricanes, extreme cold and/or floods) where genset system may not be accessible for extended periods

Applications where extended outages are expected

Benefits of Using Natural Gas in Standby Applications

The biggest advantage in using natural gas in a standby application is the availability of a reliable fuel supply. Natural gas lines produce a 24-7 supply that runs underground, meaning they are generally protected from hazardous storms, floods and hurricanes. This also eliminates the need for fuel storage tanks which require refueling, regulation and maintenance to avoid gelling and waxing in colder environments, flooding in wet climates and algae growth that can damage the system.

Operating costs for a natural gas gensets are dramatically less than diesel units. Even with the limited hours of a standby application, the savings add up quickly. A standby power system typically operates between 50 and 100 hours per year, and up to 500 hours per year at maximum. With today’s fuel pricing, a natural gas-operated standby power system utilized for only 50 hours per year can save more than $15,000 per year in fuel costs. These savings can quickly help justify the natural gas choice, either on its own or as a supplement to traditional diesel standby systems. Having the option to switch to natural gas during an extended outage can significantly reduce operating costs.

Another benefit to using natural gas is reduced exhaust emissions. The United States Environmental Protection Agency (EPA) sets limits on the amount of emissions from exhaust-producing engines, which includes generator sets. Operating on a lean mixture of fuel and air, lean-burn natural gas gensets release up to five times less NOx and virtually zero particulate matter output as compared to traditional diesel-fueled sources. Natural gas-operated generator sets equipped with air fuel ratio controls meet current EPA New Source Performance Standards and exhaust emissions criteria without additional fuel treatment for a more efficient alternative.

Analyzing Natural Gas Engines

Cat Dealers use Caterpillar’s Gas Engine Rating Pro (GERP), a PC-based software program that creates customized performance data specific to a site's altitude, ambient temperature and fuel that customers can use for analytical purposes. For an individualized data report or more information on gas powered standby products, please contact your local Cat Dealer.

Now we’d like to hear about your experience with standby natural gas generator sets.

Do you currently use natural gas engines to power your standby application? If so, tell us about it.

Would you consider using natural gas engines for your standby application? Why or why not?

Do you foresee any problems using natural gas engines in standby applications?

Is there anything Caterpillar could do to improve your experience with natural gas engines?

We have three 2.2 MW Cat generators on site, my main concern is how important is the fuel oil heater, we have above ground storage tanks. Our FOT heater 67KW heater has been disconnected, what is the reason for this heater and what issues will it cause by being disconnected? I am an HVAC mechanic by trade not a Gen. mechanic. Forgot to mention this is a data center in Virginia, not the Arctic circle.

You need to keep the fuel delivered to your engine (actually the primary fuel filters) above the "cloud point" of the fuel, ideally 5-10 degrees F above your spcified cloud point to make sure you don't start plugging filters.

Instead of heaters you could use additives, but have to be diligent in their application and maintenance. CAT Application and Installation Guide has good recommendations for fuel system design, if you don't have a copy ask you local dealer for one.

This is a bit off topic for this post, maybe you'll get more responses if you post a new thread in the appropriate section.

Yes I would have to agree with Mike, the fuel oil heaters are all about ensuring fuel delivery. That is really only a Diesel fuelling issue however, so as Mike points out maybe a little off topic here. That said, it does illustrate another area you generally don't have to worry about with the natural gas fuel options...

We have found that some N/G fired engines DO have to worry about maintaining intake or combustion air temp. Particularly up here in the GWN... Units that have remote mounted combustion air intake filter housings may have a preheating circuit of some type. For example my CM-34's pull hot water from the HT circuit to heat combustion air via a heat exchanger. This of course is another system to operate and maintain. Our 3500 series plants that draw combustion air directly from the powerhouse have found that they need to play around with air dampers/fans to keep a little heat in the building during the winter....

Guess I'll take a stab at this, although my experience is a bit dated, about 25 of my 27 years of dealership experience was primarily in the EPG business, this included prime, cogen and standby. Along with the CAT products in these applications we also serviced a large number of competative product, because we serviced a strict emissions area dealing with alternate forms of standbys was quite common. Propane and natural gas engines in standby applications had a pretty good share of our population, and we had a couple of cogen plants normally fueled with natrual gas that utilized propane as a backup fuel with automated switching. We dealt with uncontrolled, rich burn and lean burn engines.

In general, based on this experience I found overall that spark ignited engines were less reliable in standby service. My own opinion is that these engines don't tolerate no or low load operation anywhere near as well as diesl powered units of the day. While the diesels engines would slobber and smoke, they would still run and in many cases were "self correcting" if enough load was applied long enough to clean them up. SI engines tended to foul spark plugs, and the only recourse was to plug and clean or replace the spark plug. I also found that in general, mostly on smaller engines with exposed ignition systems, that other types of ignition system problems were common, such as plug lead and coil issues. Also had a number of units that would either fail to start or start and run and go too rich causeing engine damage due to fuel mixers sticking. Had some units up in local mountain areas that this problem seemed compounded by cold weather.

Now while the technology for many of these units have changed, both CI and SI, I think there are a number of factors that would drive me to still consider a CI engine over an SI engine in critical standby service. First off is transient response, while newer emissions rated diesels that are highly turbocharged don't seem to have the same transient characteristics of older diesel engines, they are still much better and have load acceptance and load rejection (an area where large SI lean burn engines can have issues) ability.

Also most newer design lean burn SI engines have very poor ability to withstand no or low load operation for any length of time, and frankly most standby systems still perform a large number of their testing run hours "off line".

Another area that is a personal pet peeve with me is comparing like model diesel to gas engines, and compare the number of things that will shut the engine down. I realize that newer gas engines have a number of parameters critical to proper engine operation, but the large number of shutdowns certainly affects its ability long term to provide reliable service, at least in my opinion.

Cold start capability is another area that can be used for comparison, low engine temperatures make a diesel unit hard to start, slow to come up to speed and causes excessive exhaust smoke and instability until it gets warmed up a bit, but it still starts and runs. Many newer lean burn gas engines, especially with pre-chamber type spark plugs, attempting a cold start is a no go and usually requires pulling and replacing plugs. While ideally w you don't want to be in that situation, it does happen fairly often.

In prime and continuos applications gas fueled engines are hard to beat, but especially with newer engine models today it seems keeping them running and on line is way better that starting and stopping, where most problems seem to occur, at least in my opinion.

While you make a number of strong points in regards to a gas fueled engine being suitable for standby service, I would think a careful review by a potential end user would weigh the actors that affect long term operation against the needs of their facility. Where i live in Southern California I worked as a technician during the Northridge earthquake, most gas lines were not in service for several days, and I spent a lot of time driving a truck with 55 gallon drums of diesel to keep facilites on line.

My own preference in many situations would be to have a diesel engine standby unit with a simple and robust dual fuel system if natural gas was available to offset fuel costs for testing and extended runs in situations such as demand response or known service outages. The unit would still have the performance characteristics of a diesel engine and the ability to use natural gas (or propane or biogas) as needed.

Mike Brings up some good points. And to his points, I would agree that Diesel Gensets will always have a place in the standby market. For example, today our Diesel product still have a significant advantage when it come to transient response. However, as Mike eludes, the gap is closing. In Dec, Cat is releasing a new series of devoted standby ratings, and two of these units (the G3516 and G3412C) have pretty stellar transient performance, especially when you compare them to other Gas product. Both of these units are capable of taking 100% block loads, and can even meet ISO 8528 deviation requirements for class G1 and G2 with factory specified load steps. Probably still not as good as the Diesel counter-part - But if this is capable of meeting your site requirements, then I would advise reviewing the other Gas advantages to determining the best option. I think the key point from my perspective is that now the gas choice is back on the table. For the longest time, I had been assuming that Diesel units were the only choice for Emergency Standby. But between the improving Gas technology, and the tightening regulations - Gas Standby has become a viable option again - at least IMHO.

For critical operations power systems, NEC 780.20 (F)(7) requires on-site fuel. Further, other codes prohibit dependance on a utility for fuel supply, cooling, or other requirments of operation. Natural gas is typically considered a utility source and not considered on-site fuel. It is best to clear this with the AHJD before commiting to natural gas.

Atcual Mike is describing our normal facility. If we have a ng or lfg engine installed they are never used as a swing engine in the island mode. The slow reaction time of NG/Lfg vs. oil dictates this requirement. These S-rice units are typically installed in a facility that already has C-rice engines For example our lfg unit is tied directly to a small distribution grid and normally runs as a base load machine to the system. In the event of an outage the LFG unit will trip and will not start again until it has a "grid" to synch to. This grid can be in the form of 12mws of duel fuel engines located in that community or reconnection to the infinite buss. IN the case of our new CM34 plant we wall use 2 x 6mw D/F engines as black start units in the event of an outage and transfer load to the big cats. While still on gas we are assured by the supplier CPGS/ISO that this new more modern gas engines will indeed operate in island mode without an oil fired engine taking the swings. They have also assured us that the new plant will be able to synch back to the grid once it returns after an outage.... I still don't believe them but we'll see I guess. It's a contract requirement so they'll be here until it works!!!

I have seen many pros and cons about the fuel used for standby applications. Sure diesel requires maintenance, but generally has better load acceptance. Natural gas is normally simpler to deal with if the genset is sized properly. But, let me throw out a simple observation based on a very real event - the Washington, Illinois, tornado of November 2013. Homes and business were demolished. Some buildings were heavily damaged. Many other buildings were indirectly affected. Because of the devastation, electrical power was cut to most of the town. And very soon after, main natural gas lines were shut off. Both of these resources were cut off because there were power lines ripped apart, and there were many open gas lines that were once connected to buildings. Within about 48 hours much of the power and gas could be restored to the indirectly affected areas because emergency crews had capped or isolated the dangerous wires and gas lines. If important buildings had natural gas generators, they were rendered useless until the gas lines could safely be turned on again. Those facilities with diesel generator sets were still able to be self sufficient until their fuel supply was used up.

My message is fundamental. The best standby genset is only as good as the supply of fuel. This is no easy winner in a diesel Vs natural gas (or propane) discussion. I believe we must also consider the availability of fuel during whatever significant event we are planning to operate through. Should we look at some sort of dual fuel power source? Should we consider a "mission critical" installation that has two different generator sets - one with on-site fuel storage (diesel), and one using a piped-in fuel (natural gas).

With all due respect, Mikel and RJKeith commented on the fuel availability issue. I am simply agreeing with their observations.

I would agree with Allentp comment. We need to understand our application, and how the "outage" scenario will affect our fuel supply need. Hurricanes and Floods present a different set of consideration than say and Earthquake scenario. One idea I've seen a couple of times in these responses is the term Dual Fuel. I curious as what experience the community has had with Dual fuel. This is certainly something Cat is looking into. Are two different gensets (Gas and Diesel) ever an option? Or are we talking about a single unit with blended fuel capability?

We have extensive experince with old tech duel fuel, about 120Mws worth of C-rice installed. For us "duel fuel" means one unit capable of running on 2 different fuels or a combination of 2 fuels. Our old tech equipment installed between @ 1948 and 1978 typically runs either 100% diesel or in the D/F mode 5-7% diesel pilot oil and 90% +- natural gas.We currently have over 30 X 3500 and 3600 series Cat engines installed today and have researched heavely into retro-fitting these units with an aftermarket ng systems however these systems typically only get to the 60/40 maybe 80/10 mix range which does make it economic to install. In todays EPA effected industry old school engines are hard to get permitted HOWEVER the EPA consideres a D/F engine with 1% or less pilot oil to be considered a SPARK fired engine and thusly easier to permit. Last year in Rostock I saw CPGS D/F engine on the test cell and I think finally they are getting their at together and gettin a DF unit to the market. After many years of being a Cat customer and telling them time after time that the will be caught out not haveing a true duel fuel engine maybe they listened. I see fule diversity mentioned several times. We actually have a back up plan to install LNG storage in our new CM34 plants should a mandate be placed on us to have a back up fule source...

LNG is an approach I'd not thought of... I suppose it would address any requirements for onsite fuel sourcing. I wonder if propane may be a better option. Many of our traditional gas product can be configured to run on both NG and Propane - Usually you'll lose a little fuel efficiency, but that may not be a big deal for a standby app. Any thoughts or experience here with propane or propane/NG in standby?

So this question is a little our of my area of expertise. Value temps issues can have a number of different root causes. I fact it is probably best addressed in a different forum or with your local dealer. Below are a couple of links that should help.

Reliable standby power provides protection in the event of power failure. For critical operations, like hospitals, data centers and water treatment plants, continuous power is essential. Standby applications inherently have limited hours of operation because they only kick on when there’s an interruption in power flow from the main source. Therefore, the more hours the dedicated standby system runs, the more important your fuel choice becomes.

The standby market is generally dominated by diesel-fueled generator sets because they can be installed with lower capital investment (per power output), and typically provide better transient (load acceptance) capabilities. Nevertheless, natural gas generator sets are gaining popularity for reliable standby power solutions thanks to ease of maintenance and reduced emissions compared to traditional diesel fuels.

Applications which may be better suited for natural gas standby gensets include:

Sites subject to tighter emission requirements

Areas that endure frequent and/or dangerous storms (hurricanes, extreme cold and/or floods) where genset system may not be accessible for extended periods

Applications where extended outages are expected

Benefits of Using Natural Gas in Standby Applications

The biggest advantage in using natural gas in a standby application is the availability of a reliable fuel supply. Natural gas lines produce a 24-7 supply that runs underground, meaning they are generally protected from hazardous storms, floods and hurricanes. This also eliminates the need for fuel storage tanks which require refueling, regulation and maintenance to avoid gelling and waxing in colder environments, flooding in wet climates and algae growth that can damage the system.

Operating costs for a natural gas gensets are dramatically less than diesel units. Even with the limited hours of a standby application, the savings add up quickly. A standby power system typically operates between 50 and 100 hours per year, and up to 500 hours per year at maximum. With today’s fuel pricing, a natural gas-operated standby power system utilized for only 50 hours per year can save more than $15,000 per year in fuel costs. These savings can quickly help justify the natural gas choice, either on its own or as a supplement to traditional diesel standby systems. Having the option to switch to natural gas during an extended outage can significantly reduce operating costs.

Another benefit to using natural gas is reduced exhaust emissions. The United States Environmental Protection Agency (EPA) sets limits on the amount of emissions from exhaust-producing engines, which includes generator sets. Operating on a lean mixture of fuel and air, lean-burn natural gas gensets release up to five times less NOx and virtually zero particulate matter output as compared to traditional diesel-fueled sources. Natural gas-operated generator sets equipped with air fuel ratio controls meet current EPA New Source Performance Standards and exhaust emissions criteria without additional fuel treatment for a more efficient alternative.

Analyzing Natural Gas Engines

Cat Dealers use Caterpillar’s Gas Engine Rating Pro (GERP), a PC-based software program that creates customized performance data specific to a site's altitude, ambient temperature and fuel that customers can use for analytical purposes. For an individualized data report or more information on gas powered standby products, please contact your local Cat Dealer.

Now we’d like to hear about your experience with standby natural gas generator sets.

Do you currently use natural gas engines to power your standby application? If so, tell us about it.

Would you consider using natural gas engines for your standby application? Why or why not?

Do you foresee any problems using natural gas engines in standby applications?

Is there anything Caterpillar could do to improve your experience with natural gas engines?